The saw-toothed grain beetle Oryzaephilus surinamensis is a serious pest of stored cereals world-wide, and the major pest of cereals in the UK. In order to combat the threat from the insect it is desirable that infestations be detected at an early stage, with concentrations of insects in grain as low as 0.1 insects per Kg (IPK) needing to be detected. The detection methods currently employed fall short of this target and require the manual inspection of samples taken from bulk grain; typically these detect above 1 IPK. In addition such methods are time consuming and labour intensive, leading to considerable expense in developed economies where labour costs are high.
These shortcomings have led to considerable interest in the production of lures for Oryzaephilus and similar pests whereby the requirement for visual inspection of grain may be eliminated. One of the most promising of these lures comprises the lactones 11-methyl-(3Z,6Z)-dodecadien-11-olide (herein referred to as II), (3Z,6Z)-dodecadien-12-olide (herein referred to as III) and 13-methyl-(5Z,8Z)-tetradecadien-13-olide (herein referred to as IV); being pheromone components of O. surinamensis, O. mercator and Cryptolestes turcicus (see Oehlschlager et al `Chemical communication in grain beetles` J. Chem. Ecol. 14, 2071 (1988). These form part of a series of structurally related macrolides (see FIG. 1) variously attractive to O. surinamensis, and four other cucujids: O. mercator, C. turcicus, C. pusillus and C. ferrugineus. The attractancy of these lactones to cucujids has led Oehlschlager and Borden to propose the generic term `cucujolides` for them. Syntheses have been published for each of these lactones and the enantiomers of four, but these do not allow for the gram scale production of either (II) 11-methyl-(3Z,6Z)-dodecadien-11-olide or (III) (3Z,6Z)-dodecadien-12-olide which are particularly targeted at O.surinamensis.
The pheromones II and III are relatively unstable even at -20.degree. C., the ring closures required to synthesise them are difficult to perform due to their highly constrained conformations and the highly unusual Z-geometry of their diene system which precludes access by elimination. Furthermore II is homochiral in activity and thus enantiospecificity is required in synthesis for maximal attractancy.
In addition to use of these pheromones, both Pierce et al (Environ. Entomol. 18, 747 (1989); J. Econ. Entomol. 83, 273 (1990)) and White at al (J. Chem. Ecol. 15. 999 (1989)) have studied the effect of the fungal volatile 1-octen-3-ol as attractant for grain beetle. Pierce et al show that 0.1 ng per pitfall olfactometer has no significant attractancy to O. surinamensis but 0.1 ng to 10 .mu.g has, while above this weight a significant repellance effect occurs. In UK strains this repellant effect takes place at as low as 100 ng per lure.
Combining a mixture of pheromones II, III and IV with the fungal volatile 1-octen-3-ol in weight ratio 1 to 4, Pierce et al showed that a lure effective across a wide range of dose levels may be provided. Further work showed that volatiles such as 3-methylbutanol (J. Chem. Ecol. 17. 581 (1991)) are also effective in synergising the action of pheromones in this manner. In these and the studies referred to above it is clear that any attractant effect is critically dependant upon the amount of each component, and that increasing or decreasing the amount of any of these can lead to repellancy for one or both sexes of the insect.